The present invention relates generally to voltage-controlled oscillators (VCO), and more particularly to degeneration (reduction) of flicker noise in VCOs.
FIG. 1 is a simplified block/circuit diagram of a conventional VCO 100. As shown, VCO 100 includes a current source 115, an LC resonant circuit 120, and cross-coupled NMOS transistors 130 and 135. For VCO 100, the resonant frequency f is determined by the following equation:
                              f          =                      1                          2              ⁢              π              ⁢                              LC                                                    ,                            (        1        )            where L and C are the inductance and capacitance of the resonant circuit 120, respectively. In some conventional systems, such as that shown in FIG. 1, the capacitance value C is varied by a control voltage signal Vctrl. In other systems, a capacitor bank with a number of fixed capacitance values is utilized in conjunction with a varactor.
Electronic oscillators typically include MOS devices which introduce noise, such as flicker noise, into the high frequency circuits. Such noise causes a random phase variation in the output oscillation, commonly known as phase noise of the oscillator. Phase noise is of concern because it degrades the signal to noise ratio and the integrity of data transmission. It is known that flicker noise is predominant at DC and low frequencies, and diminishes at higher frequencies. On the other hand, as RF design continues to advance into deep submicron technologies, the adverse effect of phase noise becomes more severe. For example, in 0.35 um technology, the flicker noise corner frequency is usually in KHz range, whereas in a 90 nm technology, the flicker noise corner frequency can be as high as MHz range. Thus, it would be desirable to provide improved methods and systems for flicker noise degeneration in a voltage controlled oscillators.